wdd_select tool for more versatile extraction

Searches for all tags matching the proviced ```CSS selector``` in
```file``` and prits a CSV with ```file,tag_name``` to ```STDOUT```.

The ```-attrs``` option can be used to provide a comma separated list of
attributes to print in the CSV.

Example:

```bash
$ wdd_select -attrs="class,id" "section, body > div" data_samples/forecast_io.html
data_samples/forecast_io.html,div,inner,""
data_samples/forecast_io.html,section,currently section,""
data_samples/forecast_io.html,section,next_hour section,""
data_samples/forecast_io.html,section,next_24_hours section,""
```